Absence Of NO Research Articles

Nitric Oxide Binding to the Ferri- and Ferroheme States of Nitrophorin 1, a Reversible NO-Binding Heme Protein from the Saliva of the Blood-Sucking Insect, Rhodnius prolixus

The recombinant NO-binding heme protein, nitrophorin 1 (NP1) from the saliva of the blood-sucking insect, Rhodnius prolixus, has been studied by spectroelectrochemistry, EPR, NMR, and FTIR spectroscopies and X-ray crystallography. It is found that NP1 readily binds NO in solution and in the crystalline state, but the protein is not readily autoreduced by excess NO. Likewise, dithionite is not a very effective reductant of NP1. However, the protein can be photoreduced by illumination with visible light in the presence of excess NO, deazaflavin, and EDTA. Optical spectra of the FeIIINO and FeIINO complexes of NP1 are extremely similar, which makes it difficult to characterize the oxidation state of the NO complex by UV−visible spectroscopy. The reduction potential of NP1 in the absence of NO is ∼300 mV more negative than that of metmyoglobin (metMb). In the presence of NO, the reduction potential shifts ∼+430 mV for NP1−NO, but the reduction potential of metMb−NO cannot be measured for comparison. Based on estimated values of Kd for NP1III−NO, the Kd values for the FeII−NO complex are 20.8 and 80.6 fM at pH 5.5 and 7.5, respectively. The lower driving force for NP1 reduction is qualitatively consistent with the slower rate of autoreduction of NP1−NO; the negative charges surrounding the heme probably also play a role in determining the much slower rate of autoreduction. The N−O stretching frequencies of NP1III−NO and NP1II−NO were measured by FTIR spectroscopy. The values obtained are very typical of other heme−NO stretching frequencies in the two oxidation states: νNO = 1917 and 1904 cm-1 for two species of FeIIINO and 1611 cm-1 for FeIINO; the values of νNO are consistent with 6-coordinate “base-on” heme−NO centers for both oxidation states. The breadths of the IR bands are consistent with the large solvent accessibility of the bound NO of NP1 and also with the possibility of minor dissociation of the protein-provided histidine ligand on the IR time scale. The ratio of the two FeIII−NO species changes with pH and the nature of the buffer. The CO complex of the Fe(II) form of NP1 has νCO = 1960 and 1936 cm-1, again showing the presence of two species. Both NMR and X-ray crystallography show that the protohemin center of NP1 imidazole has a very high preference for a single orientation of the unsymmetrical protoheme moiety. The structure shows the Fe−N−O unit to be quite bent, which is consistent with its being the FeII−NO form of the protein, presumably formed by photoreduction in the X-ray beam. The proximal base, His-59, is clearly coordinated to the iron in the crystalline state and in solution at ambient temperatures, based on FTIR data, but EPR studies of dithionite-reduced samples show that a percentage of the protein has lost the histidine ligand from the FeIINO center in frozen solution.

Flow-induced responses in skeletal muscle venules: modulation by nitric oxide and prostaglandins.

Skeletal muscle arterioles dilate in response to increases in flow velocity/wall shear stress (WSS). The effect of flow/WSS on the diameter of skeletal muscle venules and the possible endothelial mediation of the response, however, have not yet been characterized. Thus changes in diameter of pressurized (10 mmHg) and norepinephrine-preconstricted venules (179 +/- 8 micron in diameter) to increases in perfusate flow before and after endothelium removal or application of inhibitors of NO and prostaglandin (PG) synthesis, Nomega-nitro-L-arginine (L-NNA, 10(4) M) and indomethacin (Indo, 2.8 x 10(5) M), respectively, were measured. Increases in perfusate flow [elicited by increases in the pressure difference (Pdiff) between proximal and distal cannulas] evoked with a delay of 17 +/- 2 s dilations, up to 36 +/- 9 micron at the highest flow, a response that was completely eliminated by removal/disruption of the venular endothelium. Calculation of WSS indicated that in endothelium-intact venules, the midpoint of the shear stress-diameter curve was at approximately 8 dyn/cm2, whereas in endothelium-denuded vessels, shear stress increased in a linear fashion with increases in flow, up to 40 dyn/cm2. L-NNA significantly reduced flow-induced dilations (from 38 +/- 11 to 17 +/- 9 micron at 14 mmHg Pdiff), whereas in the additional presence of Indo, flow elicited constriction of venules decreasing basal diameter (by 21 +/- 8 micron at Pdiff 12 mmHg). Thus in skeletal muscle venules an increase in shear stress due to increases in perfusate flow stimulates the release of endothelium-derived NO and PGs eliciting dilation, which in turn, regulates WSS, albeit at a lower value than what is observed in arterioles. In the absence of NO and PGs, flow-induced constriction is revealed, the cause of which remains obscure. From these data, we propose that shear stress-related responses of venules are involved in the regulation of venular resistance, especially during high flow conditions, such as reactive and exercise hyperemia.

AT2 antagonist-sensitive potentiation of angiotensin II-induced constriction by NO blockade and its dependence on endothelium and P450 eicosanoids in rat renal vasculature.

1. We showed earlier that NO inhibition caused a left-shift and augmented Emax of the concentration-response curve of AT1-mediated (angiotensin II)-induced vasoconstrictions (AII-VC) in the rat kidney. The 0.01-0.1 nM AII-VC unmasked by the potentiating effect of NO inhibition, were sensitive not only to AT1 (L158809), but also to AT2 receptor (PD123319) antagonists. We now demonstrate the role of endothelium and eicosanoids in the NO-masked AT1/AT2-mediated component of the AII-VC in isolated indomethacin-perfused kidneys of the rat. 2. L-NAME increased 0.1 nM AII-VC 7.2 fold. Pretreatment of the kidneys with factor VIII antibody/complement or with the detergent CHAPS to damage endothelium, decreased carbachol-induced vasodilatation and blunted by 60 and 30% respectively, the enhancement of AII-VC during NO inhibition. 3. L-NAME also increased 3 microM noradrenaline (NA)-induced vasoconstriction (NA-VC) 8.1 fold. In contrast to AII-VC, endothelium damage was without effect on the enhancement of NA-VC by L-NAME, suggesting a dominant role of endothelium-derived NO in the enhancement of NA-VC. 4. During NO inhibition, ETYA (2 microM; an inhibitor of all arachidonic acid derived pathways) and alpha-naphtoflavone (10 microM; an inhibitor of the cytochrome P450 isozymes), decreased by 85% the 0.1 nM AII-VC. 5. In conclusion, during NO inhibition, the AT1-mediated constriction to low concentrations of AII, which is sensitive to AT2 antagonists, depends on intact endothelium, and can be blocked by inhibition of eicosanoid synthesis. The results suggest that the AII-mediated vasoconstriction through AT1 receptors is potentiated in the absence of NO, by the release of eicosanoids from the endothelium through AT2 receptors.

Nitrite production from the oxidation of salicylhydroxamic acid by peroxidase or Mn(II)

Horseradish peroxidase or green algal cells catalyzed the NADH-dependent and oxygen-consuming oxidation of salicylhydroxamic acid (SHAM) to generate NO 2 −. NO 2 − production was inhibited by superoxide dismutase or catalase. In the absence of HRP, NO 2 − could also be produced from non-enzymatic SHAM oxidation by Mn(II). These results suggest that the peroxidase activators may lead to erroneous conclusions regarding the presence of extracellular or plasma membrane nitrate reductase. Horseradish peroxidase (HRP) catalyzed the NADH-dependent and oxygen-consuming oxidation of salicylhydroxamic acid (SHAM) to generate NO 2 −. The reaction ceased when NADH was depleted, and could be re-initiated by further addition of NADH. NO 2 − production was inhibited by superoxide dismutase or catalase. Hydoxylamine could also serve as a substrate for HRP-catalyzed NO 2 − production. Selenastrum minutum, a unicellular green alga with high extracellular peroxidase activity, also produced small amounts of NO 2 − in the presence of SHAM and NADH. In the absence of HRP or algal cells, NO 2 − could also be produced from non-enzymatic SHAM oxidation by Mn(II), in a reaction that was not sensitive to inhibition by superoxide dismutase or catalase. These results suggest that under certain conditions it is possible to generate NO 2 − in the absence of NO 3 − or nitrate reductase activity, and that the commonly-employed peroxidase activators SHAM and Mn(II) may lead to erroneous conclusions regarding the presence of extracellular or plasma membrane-associated nitrate reductase.

Products of the Gas-Phase Reactions of a Series of Methyl-Substituted Ethenes with the OH Radical

Alkenes are a significant component of ambient air in urban areas, and in the atmosphere they react with OH radicals, NO3 radicals, and O3, with the OH radical reaction often dominating as the tropospheric removal process. Products of the gas-phase reactions of the OH radical with 2-methylpropene, cis-2-butene, 2-methyl-2-butene, and 2,3-dimethyl-2-butene in the presence of NO have been investigated at room temperature and 740 Torr total pressure of air by gas chromatography with flame ionization detection, in situ Fourier transform infrared absorption spectroscopy, and in situ atmospheric pressure ionization tandem mass spectrometry (API-MS). For all four alkenes, hydroxynitrate formation from the β-hydroxyalkyl peroxy radical plus NO reaction accounted for ∼10% of the overall products observed, with decomposition of the intermediate β-hydroxyalkoxy radical dominating over the alternative reaction with O2 (isomerization via a six-member transition state is not possible for any of the intermediate β-hydroxyalkoxy radicals formed in these reactions) and leading to the formation of the carbonyls expected from >CC< bond cleavage in ∼90% yield each. These data are consistent with estimates of the rates of the various reactions of β-hydroxyalkoxy radicals under atmospheric conditions. API-MS analyses of the OH radical-initiated reactions of propene, 2-methylpropene, cis- and trans-2-butene, 2-methyl-2-butene, and 2,3-dimethyl-2-butene in the absence of NO indicated the formation of the hydroxyhydroperoxides, dihydroxyalkanes, and hydroxycarbonyls expected from the reactions of intermediate β-hydroxyalkyl peroxy radicals with HO2 and organic peroxy radicals, in addition to the carbonyl compounds formed from decomposition of the β-hydroxyalkoxy radicals also formed from the peroxy plus peroxy radical reactions.

Application of the electrocatalytic reduction of nitric oxide mediated by ferrioxamine B to the determination of nitric oxide concentrations in solution

The electrocatalytic reduction of nitric oxide to nitrous oxide by the iron siderophore ferrioxamine B was used as a basis for an electrochemical NO sensor. Evaporation of a Nafion film onto a glassy carbon electrode produced modified surfaces into which the ferric complex of ferrioxamine B could be exchanged. Cyclic voltammetry of this modified electrode in aqueous solution produced two peaks, one of which (−0.73 V versus SSCE) corresponded to the quasi-reversible reduction of solution-bound ferrioxamine B and the other of which (−0.42 V) corresponded to an adsorbed species. Greater catalytic enhancement was observed in the presence of NO for the solution wave than for the adsorption pre-peak. The catalytic enhancement, expressed as the ratio of peak current in the presence of NO ( i cat) to the current in the absence of NO ( i d) was a linear function of the solution NO concentration down to 1 μM. Better sensitivity was precluded by decomposition of the reduced form of the catalyst in the absence of NO.

The effect of zeolitic protons on NO x reduction over Pd/ZSM-5 catalysts

Formation of PdO particles is observed in ion-exchanged Pd/HZSM-5 andPd/NaZSM-5 after reduction and reoxidation at 500°C. Formation of Pd 2+ ions is not observed inPd/HZSM-5 in the absence of NO x , but in an atmorphere of NO 2 + O 2 the PdO particles are transformed into Pd 2+ ions. Even inPd/NaZSM-5, roughly 20% of the PdO particles are converted to ions in NO x ; the protons needed for this process are mainly formed during reduction of Pd 2+ to Pd 0. When a reduced and reoxidizedPd/HZSM-5 catalyst is exposed to CH 4 + NO 2 + O 2, the rate of catalytic NO 2 reduction to N 2 slowly increases over 24 h from 20 to 50% while PdO is converted to Pd 2+, but the rate of CH 4 oxidation remains constant with time on-stream. Apparently, Pd 2+ ions are needed for SCR of NO x , but for methane oxidation with O 2, Pd 2+ ions and PdO particles have similar activity.Pd/HZSM-5 is active even when Pd is initially present as PdO particles, butPd/NaZSM-5 remains inactive also when part of the Pd is present as Pd 2+ ions. This shows that protons are not only required to convert PdO into Pd 2+, but also thatPd/HZSM-5 acts as a bifunctional catalyst. Possible routes for CH 4 and C 3H 8 activation are discussed.

NO is not substantially involved in afferent signalling in rat muscle spindles

As intrafusal nuclear bag and chain fibers of muscle spindles take part in both sensory and motor functions, these stretch receptors may represent a useful model to answer the question whether nitric oxide (NO) signalling is involved in sensory and motor functions or motor events only, as has already been shown for ordinary extrafusal fibers. To answer these questions, we have applied immunohistochemical and enzyme histochemical methods to serial transverse sections of the rat gastrosoleus muscle for determining the presence or absence of NOS I, NOS-associated diaphorase (NOSaD), AChE and proteins related to the dystrophin complex. NOS I, NOSaD, and AChE were practically absent from the equatorial (central) region of intrafusal fibers, i.e. the site of termination of the primary and secondary afferents. These regions showed weak staining for dystrophin, beta-dystroglycan as well as alpha- and gamma-sarcoglycan. By contrast, all of these molecules were found enriched in the polar (peripheral) regions of the intrafusal fiber sarcolemma. NOS I, NOSaD, dystrophin, beta-dystroglycan and the two sarcoglycans showed a general presence in the sarcolemma, whereas AChE was limited to the endplate region and other circumscribed areas. From these observations we would like to conclude that NO does not appear to be significantly or even not involved in signal transfer to the sensory nerve endings in the intrafusal fibers.

Isotope-selective IR multiphoton dissociation of CHClF 2 in the presence of NO 2

to the CHClF2/He mixture irradiated by a Q-switched CO2 laser leads to oxidation of the dissociation product according to the reaction: CF2+NO2→COF2+NO. The resulting COF2 with a 13C content near 50% is easy to convert to CO2 or CO for further enrichment by a nonlaser process. We measured the dependence of the fraction of dimerised CF2 on NO2 pressure pNO2 and the amount of NO2 required to suppress dimerisation on the dissociation yield. Both agree with a kinetic model using known rate constants. For the range of the dissociation parameters (13CF2 yield of 10% per pulse, isotope selectivity of 130) of practical interest, 95% of the CF2 produced is oxidized at pNO2≈1/2pCHClF2. In the absence of NO2, major (20%–35%) losses of CF2 at the metal walls of the irradiation system were observed. Addition of NO2 suppresses them. For comparison, we also used O2 as a scavenger in CHClF2 dissociation. NO2 is by orders of magnitude more efficient.

Atmospheric Chemistry of HFC-236cb: Fate of the Alkoxy Radical CF3CF2CFHO

An FTIR/environmental chamber technique was used to study the fate of the alkoxy radical CF3CF2CFHO formed in the atmospheric degradation of HFC-236cb (CF3CF2CFH2). Experiments were performed over the temperature range 228−296 K at 7.8−1000 Torr total pressure. Two reaction pathways are possible for CF3CF2CFHO radicals: reaction with oxygen, CF3CF2CFHO + O2 → CF3CF2C(O)F + HO2 (kO2) and decomposition via C−C bond scission, CF3CF2CFHO → CF3CF2 + HC(O)F (kd). CF3CF2CFHO radicals were produced by two reactions: the CF3CF2CFHO2 self-reaction and the CF3CF2CFHO2 + NO reaction. In the absence of NO at 800 Torr total pressure the rate constant ratio kd/kO2 was determined to be ( ) × 1025 exp(−(3560 ± 295)/T) molecules cm-3. The pressure dependence of kd/kO2 was studied at 238 K and was well described by a Troe type expression using kd,0/kO2 = 30.8 ± 6.9 and kd,∞/kO2 = (2.31 ± 0.12) × 1019 molecules cm-3 where kd,0 and kd,∞ are the second- and first-order rate constants for decomposition in the low- and high-pressure limits, respectively. CF3CF2CFHO radicals formed in the CF3CF2CFHO2 + NO reaction undergo more C−C bond scission than those generated in the CF3CF2CFHO2 self-reaction. This is consistent with a significant fraction ( %) of the alkoxy radicals being formed with sufficient internal energy to undergo prompt decomposition. Overall, we calculate that less than 1% of the CF3CF2CFH2 (HFC-236cb) released to the atmosphere degrades to form CF3CF2C(O)F while >99% gives CF3CF2 radicals and HC(O)F.

Mechanistic and kinetic study of formaldehyde production in the atmospheric oxidation of dimethyl sulfide

S. P. Urbanski, R. E. Stickel, Z. Zhao and P. H. Wine, J. Chem. Soc., Faraday Trans., 1997, 93, 2813 DOI: 10.1039/A701380I

Molybdenum cofactor biosynthesis in two barley ( Hordeum vulgare L.) genotypes as affected by nitrate in the tissue and in the growth medium

Two barley genotypes, the wild type and the narla, nar7w mutant, impaired in two structural genes of the nitrate reductase (NR) apoproteins, exhibited a considerable level of molybdenum cofactor (MoCo) when grown in the absence of NO 3. Increasing concentrations of nitrate in the nutrient solutions did not affect MoCo content in shoots and roots of barley plants during the first 7 h of incubation. The MoCo and pterin content of the plants remained also unchanged during 24 h induction in 0.1 mM nitrate. Removal of NO 3 − from the nutrient medium caused a rapid loss of NR activity in the shoots of wild type plants while MoCo and pterin content remained unaffected by the presence or absence of nitrate in the medium. Previous observations of MoCo induction in higher plants by NO 3 − by a number of researchers may have been due to an overestimation of the actual MoCo content due to NO 3 − accumulation in the tissue and its reduction by NADPH during the NR complementation process which resulted in nitrite accumulation. Exclusion of NADPH from the complementation medium prevented nitrite formation and allowed to estimate MoCo content in plant tissues containing a wide range of nitrate concentrations. The genotype narla:nar7w, when grown in nitrate, exhibited MoCo levels similar to that of wild type plants.

Products and mechanism of the gas-phase reaction of NO3 radicals with α-pinene

T. Berndt and O. Böge, J. Chem. Soc., Faraday Trans., 1997, 93, 3021 DOI: 10.1039/A702364B

Function and production of nitric oxide in the coronary circulation of the conscious dog during exercise.

This study determined the changes in NO production from the coronary circulation of the conscious dog during exercise. The role of endogenous NO as it relates to coronary flow, myocardial work, and metabolism was also studied. Mongrel dogs were chronically instrumented for measurements of coronary blood flow (CBF), ventricular and aortic pressure, and ventricular diameter, with catheters in the aorta and coronary sinus. Acute exercise (5 minutes at 3.6, 5.9, and 9.1 mph) was performed, and hemodynamic measurements and blood samples were taken at each exercise level. Nitro-L-arginine (NLA, 35 mg/kg IV) was given to block NO synthesis, and the exercise was repeated. Blood samples were analyzed for oxygen, plasma nitrate/nitrite (an index of NO), lactate, glucose, and free fatty acid (FFA) levels. Acute exercise caused significant elevations in NO production by the coronary circulation (46 +/- 23, 129 +/- 44, and 63 +/- 32 nmol/min at each speed respectively, P < .05). After NLA, there was no measurable NO production at rest or during exercise. Blockade of NO synthesis resulted in elevations in myocardial oxygen consumption and reductions in myocardial FFA consumption for comparable levels of CBF and cardiac work. The metabolic changes after NLA occurred in the absence of alterations in myocardial lactate or glucose consumptions. NO production by the coronary circulation is increased with exercise and blocked by NLA. The absence of NO in the coronary circulation during exercise does not affect levels of CBF, because it shifts the relationship between cardiac work and myocardial oxygen consumption, suggesting that endogenous NO modulates myocardial metabolism.

Atmospheric Oxidation of CH3Br: Chemistry of the CH2BrO Radical

The Cl-atom-initiated photooxidation mechanism of CH3Br has been investigated in chamber experiments conducted under conditions applicable to the lower atmosphere. Major carbon-containing products obtained in the presence of O2 and NO, as determined by FTIR absorption spectroscopy, are CH2O and CO. In addition, HC(O)Br is observed in the absence of NO. At low temperature, in the presence of NO, CH2BrO2NO2 was also identified as a reaction product. The results are used to determine the fate of the alkoxy radical, CH2BrO. It is found that unimolecular decomposition of CH2BrO to CH2O + Br is the dominant process in 1 atm of O2 at all temperatures studied (between 228 and 298 K), while reaction with O2, CH2BrO + O2 → HC(O)Br + HO2, and the three-centered elimination of HBr, CH2BrO → HCO + HBr, are found to be minor pathways under these conditions (less than 5% each). Assumption of a rate constant of 6 × 10-14 cm3 molecule-1 s-1 for the reaction of CH2BrO with O2 (DeMore, W. B., et al. NASA JPL Publ. 1994, No. 94-26) provides a lower limit to the rate of Br-atom elimination of 3 × 107 s-1 at 228 K, 1 atm of pressure.

The effect of O2 and NO2 on the ring retaining products of the reaction of benzene with hydroxyl radicals

The reaction of benzene with hydroxyl radicals affords phenol and 1,4-benzoquinone in 0.18±0.05 and 0.02±0.01 yield, respectively. The main reaction of the hydroxycyclohexadienyl radical with oxygen leads to the respective peroxy radical which in turn decomposes to ring cleavage products and phenol. In the presence of NO2, nitrobenzene is also formed with yields depending linearly on the initial NO2 concentration and vanishing as [NO2] approaches zero. The amount of phenol formed in the presence of NO2 is equal to that formed in the absence of NO2 within experimental error.

Product and kinetic study of the oh-initiated gas-phase oxidation of Furan, 2-methylfuran and furanaldehydes at ≈ 300 K

The products of the OH-initiated gas-phase oxidation of furan and 2-methylfuran were studied at 298 ± 2 K in the absence of NO, at 1000 mbar pressure of air using in situ long-path FTIR absorption spectroscopy to monitor reactants and products; the 254 nm photolysis of H 20 2 was used as the OH-radical source under NO. -free conditions. The major products were cis/trans-butenedial and cis/trans-4-oxo-2-pentenal for the oxidation of furan and 2-methylfuran with estimated carbon balances of ≈ 100 and ≈ 87% C, respectively. This study represents the first product determination for both furan and 2-methylfuran; a mechanism is proposed to explain the results. Rate coefficients have also been determined for the gas-phase reaction of OH radicals with the aromatic heterocyclics furan-2-aldehyde, furan-3-aldehyde, and 5-methylfurfural at 300 ± 2 K in 1000 mbar of synthetic air, using a relative kinetic technique. The rate coefficients obtained using trans-2-butene as reference compound are (units of 10 −11 cm 3 molecule −1 s −1): furan-2-aldehyde, 3.51 ± 0.11; furan-3-aldehyde, 4.85 ± 0.16; 5-methylfurfural, 5.10 ± 0.21. This study represents the first determination of the rate coefficients for these compounds.

Catalytic reactions of formate 4. A nitrite-promoted rhodium (III) catalyst for hydrogen generation from formic acid in aqueous solution

Rhodium (III) is an active homogeneous catalyst in the presence of NO 2 − for the decomposition of HCO 2H to H 2 and CO 2 in aqueous solution at 90°C. Experiments at different Rh concentrations indicate that this reactions is approximately pseudo-first-order in [Rh] suggesting mononuclear nitrorhodium complexes as the catalytically active species. The is catalyst system is gradually deactivated by reducing the soluble rhodium (III) complexes to insoluble Rh metal. Ammonia is a minor byproduct of this reaction, apparently produced by the Rh-catalyzed HCO 2H reduction of NO 2 − or NO 3 − produced by NO 2 − disproportionation. Addition of soluble Cu(II) to this reaction mixture increases drastically the NO/N 2O ration arising from the HCO 2H reduction of NO 2 −. Some noble metals other Rh also exhibit catalytic activity for formic acid decomposition in aqueous solution, particularly in the absence of NO 2 −. However, the catalytic activities of these other noble metals are considerably less than that of the NO 2 −-promoted Rh catalysic activities decreasing in the sequence Ir > Pd > Ru.

Formation of 2-Hydroxyethyl Hydroperoxide in an OH-Initiated Reaction of Ethylene in Air in the Absence of NO

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTFormation of 2-Hydroxyethyl Hydroperoxide in an OH-Initiated Reaction of Ethylene in Air in the Absence of NOShiro. Hatakeyama, Haiping. Lai, and Kentaro. MuranoCite this: Environ. Sci. Technol. 1995, 29, 3, 833–835Publication Date (Print):March 1, 1995Publication History Published online1 May 2002Published inissue 1 March 1995https://doi.org/10.1021/es00003a035RIGHTS & PERMISSIONSArticle Views84Altmetric-Citations7LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (250 KB) Get e-Alerts Get e-Alerts

Adsorption and Reactivity of No on Copper-on-Alumina Catalysts: I. Formation of Nitrate Species and Their Influence on Reactivity in No and NH 3 Conversion

The reactivity of copper-on-alumina catalysts in the reduction of NO by NH 3 + O 2 (SCR reaction) and oxidation of NH 3 to N 2 (NH 3ox reaction) as a function of the copper loading shows that (i) the specific rate of the SCR reaction per mole of copper decreases with increasing copper loading, whereas the NH 3ox reaction rate is nearly independent of the copper loading and (ii) the rate of the NH 3ox reaction is significantly higher in the absence of NO than that of the same reaction occurring during the SCR reaction. The catalysts were characterized by electron spin resonance (ESR), X-ray diffraction analysis, and UV-visible diffuse reflectance. The nature of the NO and NH 3 adsorbed species was studied using ESR and infrared (IR) spectroscopies, and IR studies of the reactive coadsorption of NO and NH 3 were carried out. The results obtained indicate that the above catalytic effects are due to the formation of nitrate species which block the reactivity of copper sites. The transformation of NO to N 2 via the intermediate formation of ammonium nitrate was shown, but the data suggest that this is only a secondary pathway of reaction responsible for the formation of N 2O as a byproduct. The nature of active copper species on the surface and the presence of competitive pathways of transformation of NO to N 2 are also discussed.